1. Field of Invention
The present invention relates to a method and system for controlling a low pressure fuel pump of a gasoline direct injection (GDI) engine for controlling a supply pressure of fuel in a GDI engine for directly injecting fuel into a combustion chamber.
2. Description of Related Art
A GDI engine is a gasoline engine for directly injecting fuel into a combustion chamber, and in order to directly inject fuel into a combustion chamber, the GDI engine boosts again a pressure of fuel that is supplied from a low pressure fuel pump that is installed in a fuel tank at a high pressure fuel pump and supplies the fuel to an injector.
The GDI engine forms a GDI engine system by combining a high pressure system that is formed with a high pressure adjustment valve, a high pressure fuel pump, a pressure sensor, and an injector and a low pressure system that is formed with a low pressure fuel pump, a fuel pump controller, and a fuel pressure sensor.
In the GDI engine system, because fuel should be injected in a high pressure into a combustion chamber, the fuel supply system further compresses the fuel in the high pressure system that has been primarily compressed in the low pressure system. Fuel that is compressed in the high pressure system is directly injected into a combustion chamber through an injector.
The GDI engine system is classified into a variable flow control method GDI engine system and a fixed flow method GDI engine system. FIG. 1 is a schematic diagram of a fuel pump controller that is applied to the variable flow control method GDI engine system.
The variable flow control method GDI engine system performs a flow control of a low pressure fuel pump with a proportional, integral, and derivative (PID) feedback control method based on a target fuel pressure value that receives from an engine control unit (ECU) and an actually measured fuel pressure value that is measured in a low pressure fuel pump.
Therefore, a flow amount that is supplied from a low pressure fuel pump of the variable flow control method GDI engine system is supplied only by the sum of a fuel pump driving minimum fuel amount and a consumed amount necessary for a given engine.
Such a variable flow control method can minimize a current amount that consumes in a fuel pump, compared with a fixed flow method of always supplying a maximum fuel amount and can obtain a fuel consumption enhancement effect.
When an almost entire segment of a general driving area is driven with a fuel pressure (e.g., 2.5 bar) of a relatively low pressure fuel pump, a vehicle to which the variable flow control method GDI engine system is applied can maximize a fuel consumption enhancement effect.
However, in some driving condition, when a fuel pressure of the low pressure fuel pump is maintained to be low, shortage of a start acceleration feeling, lighting of an engine warning lamp, and in the worst case, turn-off of starting may occur.
In order to solve such a problem, when a failure of a high pressure fuel pump is sensed, when a vehicle travels in an extremely high temperature, when a vehicle travels in an extremely low temperature, and when a vehicle travels at an extremely high region, conventional methods usually set a relatively high value (e.g., 5.0 bar) for a target fuel pressure of the low pressure side.
Although conventional methods may solve a problem when the high pressure fuel pump is actually failed, they do not solve a problem when a high pressure side fuel pressure control is failed or when a high pressure side fuel pressure control failure is estimated or detected.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.